An Engineering-Level Model of Bubble Dynamics in Centrifugal Nuclear Thermal Propulsion

This paper presents the development and validation of a computational framework for simulating gas-liquid bubble dynamics in Centrifugal Nuclear Thermal Propulsion (CNTP) systems. CNTP employs molten uranium to heat hydrogen gas, which is injected radially to produce thrust via expanding bubbles. Using Smoothed Particle Hydrodynamics (SPH), the study captures essential phenomena trends including bubble formation, void fraction evolution, and centrifugal confinement under high-gravity conditions. The pressure model integrates hydrostatic, dynamic, and Tait-like equations to simulate both static and rotating environments. The SPH framework is validated against experiments using the 'Antfarm' (static) and 'Blender II' (rotating) setups, showing good agreement in bubble velocity and rise behavior. Preliminary results from extrapolated uranium-hydrogen simulations suggest increased gas retention due to fluid properties, a factor critical to CNTP performance analysis. Ongoing efforts focus on improving model stability under rotational conditions. Rather than serving as a high-fidelity CFD tool, this model is intended as an engineering-level predictive tool — bridging the gap between detailed CFD and analytical methods — to observe behavior trends, support experimental planning, and enable early-phase system design.